Pre-war (up to 1942) 1941 Cadillac Series 63 Differential Pinion Seal Replacement Procedure

[J. Russo]

Hello All,

There are several discussions on this forum related to differential pinion seal replacement. I thought I'd document my experience in detail so that it may benefit someone contemplating the same exercise. In this post, I explain 2 options for removal and replacement of the differential pinion nut. Keep in mind that the procedure I followed was Option 1. I added Option 2 from a previous forum discussion.

Any feedback is welcome and I can adjust these procedures accordingly. Thank you in advance.

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The following explains the procedure I followed in replacing the pinion seal in my 1941 Cadillac differential. The work was done while the car was raised on jack stands. I highly recommend a lift if one is available. Thanks again to Harry Scott for guiding me through this process.

    1.    Raise the rear end at the differential and place jack stands on both ends of the axle. I learned
        to avoid raising from the frame as my leaf spring on the left side tends to flip.
    2.    For more clearance while under the car, raise the front end also.
    3. Remove 4 bolts attaching the rear of the drive shaft to the differential yoke. Move the
        driveshaft to the side and support it.
    4.    Drain the gear oil from the differential.
    5.    Spray the nut holding the differential yoke in place with penetrating oil. (Kroil, WD-40, Liquid
        Wrench, etc.)
    6.    There are different options found on the CLC forum for removing the pinion nut. I used Option 1
        with the emergency brake set.
        a. Option 1: Mark the position of the pinion nut to the pinion shaft and the differential casing
          as you will need to count the number of 360 degree turns to remove the nut. I used white out
          for the markings. However, you may need to re-apply multiple times throughout the process. A
          punch can also be used to make the marks. The markings are important as you will need to
          count the same number of turns for re-assembly.
        b. Option 2: Before you remove the pinion flange from the pinion, remove the rear wheels and
          rear brake drums. Use an in./lb. torque wrench to measure how much it takes to rotate the
          pinion. Then remove the pinion nut. For re-assembly, tighten the pinion nut until the pinion
          rotation torque is the same as before disassembly.  Do not over tighten.  If too loose or
          tight, it can cause bearing failure or differential whine.
    7.    NOTE: Clean all parts once removed. I used brake cleaner as it degreases well and evaporates
        quickly. Make special effort to clean any part that is tapped/pressed into place. Remove rough
        surfaces where contact is made by the new seal and the outer perimeter of the cup. Clean the
        yoke and shaft splines of any debris also.
    8.    There are different ways to remove the nut holding the yoke in place. I found it easiest to use
        an impact wrench with enough torque to first loosen the nut. Short bursts of the impact wrench
        in reverse to loosen the nut and track the movement. Once the nut is loose, a socket wrench can
        be used to track the remaining turns of the nut.
    9.    Remove the nut, the washer and yoke.
    10.    Removing the cup that contains the seal was the biggest challenge for me. Use a hammer and a
        punch to push the existing seal away from the inside lip of the cup. This needs to be done to
        insert a puller to remove the cup. I couldn't find a puller small enough to fit between the
        pinion shaft and the cup. I purchased a set of 3 pullers from Harbor Freight and used the
        smallest one (3 inch) to remove the cup. This is a 3-arm puller and the hooks need to face the
        outside. I also had to grind the puller arms and hooks with a bench grinder so I could get
        them small enough to fit into the cup lip without interference from the pinion shaft. Don't get
        carried away with grinding or the hooks will slip off the cup lip when tightening the puller.
    11.    Once the cup is removed, remove the old seal and clean the cup as noted above.
    12.    This is optional, but the large washer and the pinion bearing can be removed for inspection. I
        removed both, cleaned the race where the bearing is installed and soaked the bearing in gear oil
        until ready to reinstall.
    13.    My old seal was the original leather seal.
        a. Old/Original leather seal: 5/8 inch wide
        b. New seal: 3/8 inch wide. Purchased from Terrill Machine #30283.
        c. Timken seal #450117 is another option. The spec says it is ½ inch wide.
        d. Cup area where seal is installed is 1/2 inch deep. 2 ¾ inch diameter.
    14.    There is a small spring on the inside of the new seal under the rubber. This side of the seal
        faces the inner bearing. The spring has a tendency to fall out when seating the seal and or
        reinstalling the cup. Insert grease around the inside of the new seal to cover the spring under
        the rubber gasket. This will help prevent the spring from coming out when tapping the seal and
        the cup into place. I used a heavy grease.
    15.    Add Permatex #2 around the outer edge of the new seal.
    16.    The challenge with installing the #30283 seal is that it needed to be driven into an area deeper
        than the width of the seal. I used a Maddox seal driver set from Harbor freight to tap in the
        new seal, but it would not go in far enough as I didn't have a 2 3/4 inch seal driver. I also
        did not have a 2 ¾ inch socket to use as a driver. I used the smooth side of the original seal
        as a driver to fully seat the new seal. It was thick and strong enough to do the job. I then had
        to use a hook puller normally used for front wheel seals to get the original seal out. Not the
        perfect scenario but it worked.
    17.    Install the pinion bearing and large washer in that order.
    18.    Once the cup has been thoroughly cleaned and rough spots smoothed where the cup gets inserted,
        add Permatex #2 to the outer ring of the cup. Align the cup to the differential and tap it in
        evenly until fully seated.
    19.    Add Silicone RTV or pipe sealer to the splines when installing the yoke to insure there is no
        leakage.
    20.    Insert the yoke through the new seal.
    21.    Insert the washer.
    22.    Add Permatex #2 or loctite to the pinion threads and then align the nut where you removed it to
        start threading.
    23.    Turn the nut in the same number of turns used when it was removed.
    24.    Release the emergency break.
    25.    Fill the differential with gear oil.
    26.    Check for drag while turning the yoke by hand or with a wrench to determine if an adjustment is
        needed. As noted above, do not over tighten the pinion nut.  If too loose or too tight, it can
        cause bearing failure or differential whine.
    27.    Re-install the drive shaft at the yoke.
    28.    Another check after installation is a test drive. I drove for 30 miles, listening for any
        unusual sounds or performance issues. Once stopped, I immediately used a laser thermometer to
        check the temperature of the differential. The laser was pointed at the cup (111 degrees), the
        area of the differential where the bearing is positioned (130 degrees), rear of the differential
        (112 degrees).
    29.    Remember also to check for leaks. Fortunately for me I found no leaks.

[Jay Friedman]

Excellent write up.  I saved it for future use if necessary.